c# parse string to float

LabR@t · 3 Apr 2009 at 14:33

i need to parse a string which the user has inputed to a float value so I can do some calculations on it. But it kind of got me stumped .
any ideas?

Whitman · 3 Apr 2009 at 14:47

A quick google reveals:

Code:

string str = "3.14159";
float fnum = float.Parse(str);

LabR@t · 3 Apr 2009 at 17:20

cool thx that stumped me and i must have been googling wrong , anyway thanks

EvilOne · 3 Apr 2009 at 18:01

LabR@t said:
must have been googling wrong

Its always the simple things that that happans on too

lol.

MonkieMann · 9 Apr 2009 at 12:34

you might want to use this instead, unless you know that your string is going to be a valid float value:

Code:

string str = "3.14159";
float fnum;
bool result = float.TryParse(str, out fnum);

TryParse will return true if string is valid, and false if not, and irc, this will also set fnum to zero if the string isn't a valid float value, the other code would just throw an exception

oh and don't miss out the out

Pho · 9 Apr 2009 at 12:40

^ You could also wrap it up in a try/catch and catch the FormatException.

MonkieMann · 9 Apr 2009 at 12:47

Pho said:
^ You could also wrap it up in a try/catch and catch the FormatException.

yes you could

depends on your style of coding though I guess, I prefer the method I use but the guys in the office prefer the try catch method because it easier to see what's going on

Inquisitor · 9 Apr 2009 at 14:05

MonkieMann said:
yes you could depends on your style of coding though I guess, I prefer the method I use but the guys in the office prefer the try catch method because it easier to see what's going on

Generally you should use float.Parse if you're expecting input to be valid and if invalid input will cause terminal problems, and float.TryParse if invalid input is expected/won't cause problems. It's a matter of semantics really though.

Goksly · 12 Apr 2009 at 14:31

Pho said:
^ You could also wrap it up in a try/catch and catch the FormatException.

Exceptions are fairly expencive, so I think its not only 'better looking' but more efficient to use tryparse.

Inquisitor · 12 Apr 2009 at 14:54

Goksly said:
Exceptions are fairly expencive, so I think its not only 'better looking' but more efficient to use tryparse.

While I agree that exceptions probably aren't the way to go here, I'd disagree that performance is a valid reason; exceptions are not as expensive as people think, and avoiding them for the sake of performance is almost always premature optimization. Have a read:

http://www.yoda.arachsys.com/csharp/exceptions2.html

UK|AL · 12 Apr 2009 at 17:22

I prefer exceptions to return codes, you can put more information in an exception, and it leaves all the if(status == 1) statements out.

Goksly · 13 Apr 2009 at 20:37

Inquisitor said:
While I agree that exceptions probably aren't the way to go here, I'd disagree that performance is a valid reason; exceptions are not as expensive as people think, and avoiding them for the sake of performance is almost always premature optimization. Have a read:

http://www.yoda.arachsys.com/csharp/exceptions2.html

I've done my own tests and in situations where exceptions are thrown on a regular basis, the performance is terrible. If I remember my figures from a test (took a big file with ~10m piece of information - roughly 30% were not numbers, and recorded how long it took tryparse and exceptions to churn through it). The tryparse method was about 50x faster or somewhere abouts.

Basically exceptions (imo) should be thrown in exceptional situations only. If there is something to do with user input or a half decent chance unexpected data could be coming in I will always check the data rather than relying on exceptions.

I guess the main point is in many situations the number of exceptions won't cause performance issues as it might be a stand alone app, but on a website with thousands of users or something time critical, it wouldn't be a great idea.

all imo :}